Effects of Cooling Rate on Hot-Cracking Susceptibility of Cu-Ni-Si Alloys

The hot-cracking susceptibility of Cu-Ni-Si alloys was quantitatively evaluated through an I-beam test for the first time. The test results of the two cooling conditions changed as functions of the mold temperature, and the minimum restraint distance necessary for hot cracking increased as the cooling rate decreased. The pressure drop in the liquid phase at the dendrite gap was calculated from the test results using the Rappaz–Drezet–Gremaud (RDG) model. By comparing the calculated pressure drop to the cavitation depression, the appropriate coalescence solid fraction to reproduce the experimental results was estimated to be 0.918–0.919 and 0.906–0.921 under rapid (21.8–21.9°C/s) and slow (4.1–6.9°C/s) cooling conditions, respectively. No significant difference was observed in the coalescence solid fraction, at which the dendrite branches merges, between the two cooling conditions used in this study.